We will study the role of colostrum/breast milk in the host defense of the GI tract. Our overall hypothesis is that breast milk contains factors that can actively stimulate the development of normal intestinal mucosal barrier function in the newborn. Specifically we plan to define factors in breast milk/amniotic fluid which may: 1) influence the expression of class II antigens on immature enterocytes; 2) affect enterocyte microvillus membrane glycosylation and bacterial colonization and 3) influence the expression of a fetal human small intestinal Fc receptor (FcR) for maternal IgG. We will also develop an immortal human fetal small intestinal cell line to study these intestinal immaturities and the effect of growth modulators on their maturation at the cellular/molecular level. During the previous funding period, we have shown that: 1) maternal food antigens can enter breast milk and cause colitis in some infants in the presence of breast milk lymphocytes and cytokines; 2) that enterocytes from neonatal mice will express class II (Ia) antigens after weaning; and 3) that this expression can be prematurely displayed in the presence of inflammatory cytokines (gammaINF). In addition, we demonstrated that numerous non-immune host defenses (MVM fluidity, antigen uptake, response to bacterial toxins and bacterial colonization) are immature in the neonatal intestine and these immaturities may be due to altered MVM protein/lipid composition, glycosylation of glycoproteins/glycolipid and post receptor signal transduction. We also provide preliminary evidence that "growth factors" in breast milk can induce a maturation of enterocyte immaturities resulting in a decrease in the incidence of neonatal intestinal diseases (necrotizing enterocolitis and toxigenic diarrhea). Finally, we have provided preliminary evidence that a "Fc" receptor for IgG antibodies exists in the 18-20 week human fetal intestine (before the placental "Fc" develops). The human fetal intestinal FcR may be important in the passive transfer of maternal IgG from amniotic fluid and preterm breast milk to the fetal/neonatal circulation. To accomplish the planned research we have begun in vitro studies in intestinal cell lines and primary human enterocyte organ/cell cultures of fetal, neonatal and infant intestine and have begun studies to transfect fetal human intestinal cells with viral oncogenes to render them immortal and capable of differentiation. Molecular approaches will be used to define in enterocyte the role of growth modulators on: 1) the transcription and translation of class II antigens; 2) the glycosyltransferase enzyme activities in fetal/neonatal humans vs. older children; and 3) the association of immature glycosylation on bacterial adherence to intestinal glycoconjugates; 4) the mRNA/enzymatic activity of glycosyltransferase. Finally, we will try to isolate and characterize the human fetal FcR on the small intestine, produce monoclonal antibodies against it and then define its cDNA clone to determine the ontogeny of the receptor as a function of age, identify developmental factors which may affect this gene's expression (intrauterine infection, cytokines in amniotic fluid/breast milk) and evaluate its functional significance as a shuttle for maternal IgG antibodies.